Named queries

Hi

I've added the concept of "Named Queries": statements that can be pre-defined in a specified properties file and looked up by name; these can be executed directly as queries or updated using `ExecuteNamedQuery "<name>"` or `ExecuteNamedUpdate "<name>"` if they do not contain parameters.

If you have JDBC parameters in the query (? markers) then you should use `FetchNamedQuery` to lookup the query and create a prepared statement, then use a series of `Add<Type>Parameter value="<value>"` steps, followed by `ExecuteQuery` or `ExecuteUpdate` depending on the type of statement.

I have implemented as many `Add<Type>Parameter` steps as there are type converters in the substeps-api project (but these don't appear to handle `null`s well, so I have also created `Add<Type>Parameter value=null` steps (note the lack of quotation marks))

There is basic testing around the substeps, but this should be improved, as should the handling of escaped quotes within values.

I hope that's all OK.

Alan